1. Field of the Invention
The present invention relates in general to integrated circuit (IC) manufacturing and, more specifically, to methods in IC manufacturing processes for sorting IC devices using identification (ID) codes, such as fuse IDs, in the devices.
2. State of the Art
Integrated circuits (ICs) are small electronic circuits formed on the surface of a wafer of semiconductor material, such as silicon, in an IC manufacturing process referred to as “fabrication.” Once fabricated, ICs are electronically probed to evaluate a variety of their electronic characteristics, cut from the wafer on which they were formed into discrete IC dice or “chips,” and then assembled for customer use using various well-known IC packaging techniques, including lead frame packaging, Chip-On-Board (COB) packaging, and flip-chip packaging.
Before being shipped to customers, packaged ICs are generally tested to ensure they will function properly once shipped. Testing typically involves a variety of known test steps, such as pre-grade, burn-in, and final, which test ICs for defects and functionality and grade ICs for speed. As shown in FIG. 1, ICs that pass the described testing are generally shipped to customers, while ICs that fail the testing are typically rejected.
The testing standards for a particular IC product are sometimes relaxed as the product “matures,” such that ICs previously rejected under strict testing standards may pass the relaxed testing standards. Consequently, reject bins containing previously rejected ICs are sometimes “culled” for ICs that are shippable under relaxed testing standards by testing the rejected ICs again using the relaxed testing standards. Unfortunately, while this culling process does retrieve shippable ICs from reject bins, it makes inefficient use of expensive and often limited testing resources by diverting those resources away from testing untested ICs in order to retest previously rejected ICs. Therefore, there is a need in the art for an improved method of culling or sorting such reject bins for shippable ICs.
Similarly, as shown in FIG. 2, all the ICs from the wafers in a wafer lot typically undergo enhanced reliability testing that is more extensive and strict than normal testing when any of the wafers in the lot are deemed to be unreliable because of fabrication or other process errors. Since a wafer lot typically consists 50 or more wafers, many of the ICs that undergo the enhanced reliability testing do not require it because they come from wafers that are not deemed unreliable. Performing enhanced reliability testing on ICs that do not need it is inefficient because such testing is typically more time-consuming and uses more resources than normal testing. Therefore, there is a need in the art for a method of sorting ICs from a wafer lot into those ICs that require enhanced reliability testing and those that do not.
Likewise, as shown in FIG. 3, a new or special “recipe” for fabricating ICs on wafers is sometimes tested by fabricating some wafers from a wafer lot using the special recipe and other wafers from the wafer lot using a control recipe. ICs from the wafers then typically undergo separate assembly and test procedures so that the test results of ICs fabricated using the special recipe are not mixed with the test results of ICs fabricated using the control recipe, and vice versa. Test reports from the separate test procedures are then used to evaluate the special recipe and to determine whether the ICs are to be shipped to customers, reworked, repaired, retested, or rejected. Unfortunately, because the ICs undergo separate test and assembly procedures, undesirable variables, such as differences in assembly and test equipment, are introduced into the testing of the special recipe. It would be desirable, instead, to be able to assemble and test the ICs using the same assembly and test procedures, and to then sort the ICs and their test results into those ICs fabricated using the special recipe and those ICs fabricated using the control recipe. Therefore, there is a need in the art for a method of identifying individual ICs fabricated using a special or control recipe and sorting the ICs based on their fabrication recipe.
As described above, ICs are typically tested for various characteristics before being shipped to customers. For example, as shown in FIG. 4, ICs may be graded in test for speed and placed in various bins (e.g., 5 nanoseconds (ns), 6 ns, and 7 ns bins) according to their grading. If a customer subsequently requests a more stringent speed grade (e.g., 4 ns), ICs in one of the bins (e.g., a 5 ns bin) are retested and thereby sorted into ICs that meet the more stringent speed grade (e.g., 4 ns bin) and those that do not (e.g., 5 ns bin). While this conventional process sorts the ICs into separate speed grades, it makes inefficient use of expensive and often limited testing resources by diverting those resources away from testing untested ICs in order to retest previously tested ICs. Therefore, there is a need in the art for an improved method of culling or sorting bins for ICs that meet more stringent standards, such as a higher speed grading.
As described in U.S. Pat. Nos. 5,301,143, 5,294,812, and 5,103,166, some methods have been devised to electronically identify individual ICs. Such methods take place “off” the manufacturing line and involve the use of electrically retrievable ID codes, such as so-called “fuse IDs,” programmed into individual ICs to identify the ICs. The programming of a fuse ID typically involves selectively blowing an arrangement of fuses and anti-fuses in an IC so that when the fuses or anti-fuses are accessed, they output a selected ID code. Unfortunately, none of these methods address the problem of identifying and sorting ICs “on” a manufacturing line.